Apparatus for transferring traction forces exerted on an implantable medical lead

ABSTRACT

A medical electrical lead that includes a lead body having a plurality of lead body lumens, an electrode head assembly fixedly engaged with the lead body, a first conductor extending within a first lead body lumen of the plurality of lead body lumens, and a first electrode, positioned along the electrode head assembly, having a deformation coupling the first electrode to the first conductor and transferring traction forces applied to the lead body to the electrode head assembly. A second electrode extends along the electrode head assembly and the lead body and a second conductor extends within a second lead body lumen of the plurality of lead body lumens. An attachment member couples the second electrode and the second conductor and transfers traction forces applied to the lead body to the electrode head assembly

REFERENCE TO PRIORITY APPLICATION

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/284,430, entitled “MEDICAL ELECTRICAL LEAD”,incorporated herein by reference in its entirety.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] Cross-reference is hereby made to commonly assigned related U.S.Applications, filed concurrently herewith, docket number P-10009,entitled “INSULATING MEMBER FOR A MEDICAL ELECTRICAL LEAD AND METHOD FORASSEMBLY”; P-10010, entitled “DRIVE SHAFT SEAL FOR A MEDICAL ELECTRICALLEAD”; P-10012, entitled “IMPLANTABLE MEDICAL LEAD HAVING A RETRACTIONSTOP MECHANISM”; and P-10051, entitled “MEDICAL ELECTRICAL LEAD”.

FIELD OF THE INVENTION

[0003] The present invention relates generally to a medical electricallead, and, more particularly, the present invention relates to anapparatus for transferring traction forces exerted on an implantablemedical electrical lead.

BACKGROUND OF THE INVENTION

[0004] A wide assortment of implantable medical devices (IMDs) arepresently known and in commercial use. Such devices include cardiacpacemakers, cardiac defibrillators, cardioverters, neurostimulators, andother devices for delivering electrical signals to a portion of the bodyand/or receiving signals from the body. Pacemakers, for example, aredesigned to operate so as to deliver appropriately timed electricstimulation signals when needed, in order to cause the myocardium tocontract or beat, and to sense naturally occurring conduction signals inthe patient's heart.

[0005] Devices such as pacemakers, whether implantable or temporaryexternal type devices, are part of a system for interacting with thepatient. In addition to the pacemaker device, which typically has someform of pulse generator, a pacing system includes one or more leads fordelivering generated stimulation pulses to the heart and for sensingcardiac signals and delivering those sensed signals back to thepacemaker. As is known, pacemakers can operate in either a unipolar orbipolar mode, and can pace the atria or the ventricles. Unipolar pacingrequires a lead having only one distal electrode for positioning in theheart, and utilizes the case, or housing of the implanted device as theother electrode for the pacing and sensing operations. For bipolarpacing and sensing, the lead typically has two electrodes, a tipelectrode disposed at the distal end of the lead, and a ring electrodespaced somewhat back from the distal end. Each electrode is electricallycoupled to a conductive cable or coil, which carries the stimulatingcurrent or sensed cardiac signals between the electrodes and theimplanted device via a connector.

[0006] Combination devices are available for treating cardiacarrhythmias that are capable of delivering shock therapy, forcardioverting or defibrillating the heart in addition to cardiac pacing.Such a device, commonly known as an implantable cardioverterdefibrillator or “ICD”, uses coil electrodes for delivering high-voltageshock therapies. An implantable cardiac lead used in combination with anICD may be a quadrapolar lead equipped with a tip electrode, a ringelectrode, and two coil electrodes. A quadrapolar lead requires fourconductors extending the length of the lead body in order to provideelectrical connection to each electrode.

[0007] In order to perform reliably, cardiac pacing leads need to bepositioned and secured at a targeted cardiac tissue site in a stablemanner. One common mechanism for securing an electrode position is theuse of a rotatable fixation helix. The helix exits the distal end of thelead and can be screwed into the body tissue. The helix itself may serveas an electrode or it may serve exclusively as an anchoring mechanism tolocate an electrode mounted on the lead adjacent to a targeted tissuesite. The fixation helix may be coupled to a drive shaft that is furtherconnected to a coiled conductor that extends through the lead body asgenerally described in U.S. Pat. No. 4,106,512 to Bisping et al. Aphysician rotates the coiled conductor at a proximal end to causerotation of the fixation helix via the drive shaft. As the helix isrotated in one direction, the helix is secured in the cardiac tissue.Rotation in the opposite direction removes the helix from the tissue toallow for repositioning of the lead at another location.

[0008] Removal of a chronically implanted lead is sometimes necessary,for example, due to a medical complication associated with the implantedlead system or due to the need to implant a new type of lead system.However, after a lead has been implanted in a patient's body for aperiod of time, fibrotic tissue growth typically encapsulates the lead,strongly adhering the lead to the surrounding tissue. As a result,considerable traction applied to the proximal end of the lead may benecessary to pull the lead free. Reinforcement of some type, extendingalong the lead body, is beneficial in preventing breakage or partialdisassembly of the lead during extraction. Several such reinforcementmechanisms are disclosed, for example, in U.S. Pat. No. 5,231,996 toBardy et al.

[0009] In the context of implantable cardiac leads, the use of cabled orstranded conductors in place of commonly used coiled conductors providesincreased tensile strength. Exemplary cabled or stranded conductors aredisclosed in U.S. Pat. No. 5,760,341 issued to Laske et al., and U.S.Pat. No. 5,246,014 to Williams et al. The improved tensile strengthexists substantially between the electrode and the connector that thecabled or stranded conductor is coupled between.

[0010] In leads having an active fixation device, such as a fixationhelix, the fixation device is generally housed in a relatively rigidelectrode head member to provide support needed in securing the fixationdevice within the body tissue. The rigid electrode head member iscoupled to a lead body that is more flexible for allowing easier passagethrough the cardiovascular structures. To improve the extractability ofa lead of this type, it is desirable to transfer tensile force directlyto the relatively rigid electrode head. Providing features that make alead easier to extract allows the clinician to complete the associatedsurgical procedure more safely and in less time.

SUMMARY OF THE INVENTION

[0011] The present invention is directed to a medical electrical leadincluding a lead body having a plurality of lead body lumens, and anelectrode head assembly fixedly engaged with the lead body. A firstconductor extends within a first lead body lumen of the plurality oflead body lumens, and a first electrode is positioned along theelectrode head assembly, and has a deformation coupling the firstelectrode to the first conductor and transferring traction forcesapplied to the lead body to the electrode head assembly.

[0012] In accordance with another aspect of the present invention, themedical electrical lead includes a second electrode extending along theelectrode head assembly and the lead body, a second conductor extendingwithin a second lead body lumen of the plurality of lead body lumens,and an attachment member coupling the second electrode and the secondconductor and transferring traction forces applied to the lead body tothe electrode head assembly.

[0013] By coupling the conductors to the electrode head assembly, thepresent invention enables traction forces applied to the proximal end ofthe lead body to be transferred to the electrode head assembly via thecabled conductors rather than to the electrodes, the coiled conductor orthe joint between the electrode head assembly and the lead body. Byproviding at least two cable connections to the electrode head assembly,redundant reinforcement is provided ensuring tensile integrity of thelead even if one cable connection should fail. Thus, features includedin the present invention improve the reliability and durability of animplantable medical lead during extraction.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a plan view of an implantable cardiac lead that may beutilized in accordance with the present invention;

[0015]FIG. 2 is a cross-sectional view of a multi-lumen lead body shownin FIG. 1;

[0016]FIG. 3 is a side cut away view of a distal end of the lead shownin FIG. 1 showing a cable connected to a ring electrode and an electrodehead assembly;

[0017]FIG. 4 is a side, cut-away view of the distal end of the leadshown in FIG. 1 showing a second cable connected to a coil electrode andthe electrode head assembly;

[0018]FIG. 5 is a perspective view of an attachment member used forinterlocking with a coil electrode and a cable in a distal end of a leadaccording to the present invention; and,

[0019]FIG. 6 is a perspective view of the electrode head assemblyaccording to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0020]FIG. 1 is a plan view of a lead that may be utilized in accordancewith the present invention, embodied as a transvenous cardiacdefibrillation lead. As illustrated in FIG. 1, a lead 10 according tothe present invention includes an elongated lead body 12 having aconnector assembly 16 at a proximal end of the lead 10 for connecting toan implantable device, and an electrode head assembly 14 at a distal endof the lead 10 for carrying one or more electrodes. Lead 10 is shown asa quadrapolar lead including, at or near the distal end, a helical tipelectrode 30, a ring electrode 50, a right ventricular (RV)defibrillation coil 38 and a superior vena cava (SVC) defibrillationcoil 40. The helical tip electrode 30 and ring electrode 50 may beutilized to sense cardiac signals and/or deliver pacing pulses to apatient. One of the defibrillation coils 38 or 40 serves as the cathodewhile the other serves as the anode during delivery of a defibrillationshock to a patient as a result of a detected tachycardia or fibrillationcondition.

[0021] The lead body 12 takes the form of an extruded tube ofbiocompatible plastic such as silicone rubber. Multiple lumens locatedwithin the lead body 12 carry four insulated conductors from theconnector assembly 16 to the corresponding electrodes 30, 50, 38 and 40located at or near the distal end of the lead 10. The multi-lumen leadbody 12 may correspond generally to that disclosed in U.S. Pat. No.5,584,873 issued to Shoberg et al., incorporated herein by reference inits entirety. Three of the insulated conductors carried by lead body 12are preferably stranded or cabled conductors, each electrically coupledto one of the ring electrode 50, the RV coil 38 and the SVC coil 40. Thecabled conductors are preferably inextensible or minimally extensibleand may correspond generally to the conductors disclosed in U.S. Pat.No. 5,246,014, issued to Williams et al., incorporated herein byreference in its entirety. A fourth, coiled conductor extends the lengthof the lead body 12 and is coupled to the helical tip electrode 30.

[0022] In this embodiment, the helical tip electrode 30 functions as anelectrode for cardiac pacing and/or sensing and as an active fixationdevice for anchoring the lead 10 in a desired position. In otherembodiments that may employ the present invention, a helical tip mayfunction only as an active fixation device. Therefore, the helical tipelectrode 30 may also be referred to herein as a “fixation helix.” Inother embodiments, the lead 10 may possess other types of passive oractive fixation mechanisms, such as hooks or tines.

[0023] The connector assembly 16 has multiple connector extensions 18,20, and 22 arising from a trifurcated connector sleeve, typically formedof silicone rubber. The connector extensions 18, 20, and 22 couple thelead 10 to an implantable medical device such as an implantablecardioverter defibrillator (ICD).

[0024] Connector extension 20 is shown as a bipolar connector includinga connector ring 24 and a connector pin 25. Connector extension 20houses the cabled conductor that is electrically coupled to theconnector ring 24 at the proximal lead end and to the ring electrode 50at the distal lead end. The connector extension 20 also houses thecoiled conductor that is electrically coupled to the connector pin 25and extends to the tip electrode 30. During a lead implant or explantprocedure, rotation of the connector pin 25 relative to the connectorassembly 16 causes corresponding rotation of the coiled conductor andadvancement or retraction of the helical tip electrode 30 in the fashiongenerally described in U.S. Pat. No. 4,106,512 to Bisping et al.,incorporated herein by reference in its entirety. By advancing thehelical tip electrode 30, the electrode 30 can be actively fixed incardiac tissue. A stylet 32 may be advanced within an inner lumen of thecoiled conductor to the distal end of the lead 10 to aid in leadplacement during an implant procedure.

[0025] The connector extension 18 carries a single connector pin 52 thatis electrically coupled to an insulated cable extending the length ofthe lead body 12 and electrically coupled to the RV coil 38. Theconnector extension 22 carries a connector pin 42 that is electricallycoupled to a respective insulated cable that is further coupled to theSVC coil 40.

[0026]FIG. 2 is a cross-sectional view of a multi-lumen lead body of thelead of FIG. 1. As illustrated in FIG. 2, the lead body 12 includes fourlumens 102, 122, 124, and 126. Lumen 102 carries the coiled conductor 26that is coupled to the helical tip electrode 30. The conductor 26 isshown surrounded by insulation tubing 120. A stylet 32 may be advancedwithin the lumen 34 of the coiled conductor 26 during implantationprocedures. Lumen 122 carries an insulated cable conductor 110 that iselectrically coupled at a proximal end to the connector ring 24 and at adistal end to the ring electrode 50. Lumen 124 carries an insulatedcable conductor 112 that is electrically coupled at a proximal end tothe connector pin 52 and at a distal end to the RV coil 38. Lumen 126carries an insulated cable conductor 114 that is electrically coupled ata proximal end to the connector pin 42 and at a distal end to the SVCcoil 40.

[0027]FIG. 3 is a side cutaway view of the distal end of the lead 10showing a detailed view of the electrode head assembly 14 and theelectrodes 30, 50 and 38. The molded, tubular electrode head assembly 14includes two members, a distal electrode head assembly 113 and aproximal electrode head assembly 111. The distal and proximal electrodehead assemblies 113 and 111 are preferably formed from a relativelyrigid biocompatible plastic. For example, assemblies 113 and 111 may befabricated from molded polyurethane. The proximal electrode headassembly 111 is coupled to the multi-lumen lead body 12, typicallyformed from a relatively more compliant plastic such as silicone rubber,at a joint 140. The lumen 104 within the proximal electrode headassembly 111 communicates with the lumen 102 within the lead body 12 forcarrying the coiled conductor 26 extending between the tip electrode 30and the connector ring 24. In FIG. 3, the ring electrode 50 is showncoupled to the cable 110, and the RV coil 38 is shown positioned on theouter diameter of the proximal electrode head assembly 111 and the leadbody 12.

[0028]FIG. 3 further shows the helical tip electrode 30 electricallycoupled to the coiled conductor 26 via a drive shaft 100. The electrode30 and drive shaft 100 are preferably fabricated of a biocompatiblemetal such as platinum iridium alloy. The coiled conductor 26 extends tothe proximal connector assembly 16. Rotation of the connector pin 25 atthe proximal end of coiled conductor 26 causes corresponding rotation ofthe distal end of the coiled conductor 26 to, in turn, cause rotation ofthe drive shaft 100. This rotation results in extension or retraction ofhelical tip electrode 30. A guide 28 actuates the helical tip 30 as itis advanced or retracted. The lead 10 may include a drive shaft seal 109encircling the drive shaft 100. The drive shaft seal 109, which may beformed of silicone or any other elastomer, is housed within the proximalelectrode head assembly 111.

[0029] According to the present invention, as illustrated in FIG. 3, thering electrode 50 is coupled to the cable 110 via two deformations 220.During assembly, a tool is used to press the ring electrode 50 againstthe cable 110 creating indentations or crimp-like deformations 220,which ensure the electrical coupling of the ring electrode 50 to thecable 110. Ring electrode 50 is captured between the proximal and distalelectrode head assemblies 111 and 113 when the assemblies 111 and 113are bonded together. In this way, traction forces applied at theproximal lead end are transferred to the electrode head assembly 14 inpart via the cable 110 that is coupled to the ring electrode 50 viadeformations 220.

[0030] As illustrated in FIGS. 3 and 4, the RV coil 38 is positioned onan outer surface 140 of the proximal electrode head assembly 111 and thelead body 12. As illustrated in FIG. 4, a cross-groove crimp sleeve, orattachment member 224, provides electrical connection of cable 112 tothe RV coil 38 and mechanical connection to the proximal electrode headassembly 111. The attachment member 224 is fabricated of a conductivebiocompatible metal such as titanium or platinum. The attachment member224 provides a tubular portion for receiving the cable 112 and a groove,running perpendicular to the tubular portion, for receiving one or morecoils of RV coil 38 in a manner as generally described in U.S. Pat. No.5,676,694 to Boser et al., and in U.S. Pat. No. 6,016,436 to Bischoff etal., both patents incorporated herein by reference in their entirety.

[0031]FIG. 5 is a perspective view of an attachment member forinterlocking with a coil electrode and a cable in a distal end of alead, according to the present invention. As illustrated in FIG. 5, theattachment member 224 according to the present invention includes across-groove 228 for receiving one or more coils of RV coil 38 and atubular receiving portion 226 having a lumen 232 for receiving the cableconductor 112. The RV coil 38 may be welded or brazed within the groove228. Alternatively, this connection may be made by crimping or otherwisecompressing the groove 228 around RV coil 38 to provide an electricaland mechanical coupling to the coil 38. The cable 112 may be coupled tothe attachment member 224 by crimping the receiving portion 226, orstaking, welding, brazing or otherwise mechanically and electricallycoupling the cable 112 to the sleeve 224.

[0032]FIG. 6 is a perspective view of a proximal electrode head assemblyaccording to the present invention. As illustrated in FIG. 6, theproximal electrode head assembly 111 includes a recess 234 for retainingthe attachment member 224. The attachment member 224 is maintainedwithin the recess 234 by a biocompatible plastic tube surrounding theproximal end 239 of the assembly 111. The RV coil 38 is positioned overthe proximal end 239 with one or more coils interlocking withcross-groove 228 of the attachment member 224 (FIG. 5) residing inrecess 234. A second recess 236 is provided for retaining the cable 110that is coupled to ring electrode 50, which is positioned over thedistal end 238 of the assembly 111. The deformations 220 (FIG. 3)electrically couple the ring electrode 50 to the cable 110 residing inrecess 236 and thereby couple the cable 110 to the electrode headassembly 14 once the ring electrode 50 is captured between proximal anddistal electrode head assemblies 111 and 113 as shown in FIG. 3.

[0033] In addition, as illustrated in FIG. 6, the recess 234 includes anopening so that once attachment member 224 is inserted within the recess234, opening 235 is adjacent to the lumen 232 so that the cableconductor 112 is inserted within opening 235 and lumen 232 andpositioned at the receiving portion 226.

[0034] Thus, two connections are provided to the electrode head assembly14, one by the cable 110 residing in recess 236 coupled to ringelectrode 50 and the other by the cable 112 interlocking with theattachment member 224 residing in recess 234. This double connection tothe electrode head assembly from the cables 110 and 112, which extendproximally to connector assembly 16, provides improved tensile strengthto lead 10 for better withstanding extraction forces applied during leadremoval. Traction forces applied to the proximal end of lead 10 will betransferred via the cables 110 and 112 to the electrode head assembly111, preventing separation of lead body 12 from the electrode headassembly 111 or other lead breakage. A redundant lead strengtheningmechanism is provided by having two cable connections to the electrodehead assembly 14 so that, should one connection fail, the remainingconnection will prevail, thereby ensuring tensile integrity of the lead10.

[0035] The lead described above with respect to the present invention isa quadrapolar high-voltage lead of the type that may be used inconjunction with an implantable cardioverter defibrillator. However, itwill be understood by one skilled in the art that any or all of theinventive aspects described herein may be incorporated into other typesof lead systems. For example, one or more of the aspects may be includedin a multipolar pacing lead having any combination of a tip electrode,one or more ring electrodes, and/or one or more coil electrodes for usein pacing, sensing, and/or shock delivery. Alternatively, drug-deliveryor other electrical stimulation leads may employ aspects of the presentinvention for improving the lead extraction characteristics. As such,the above disclosure should be considered exemplary, rather thanlimiting, with regard to the following claims.

What is claimed is:
 1. A medical electrical lead, comprising: a leadbody having a plurality of lead body lumens; an electrode head assemblyfixedly engaged with the lead body; a first conductor extending within afirst lead body lumen of the plurality of lead body lumens; and a firstelectrode, positioned along the electrode head assembly, having adeformation coupling the first electrode to the first conductor andtransferring traction forces applied to the lead body to the electrodehead assembly.
 2. The medical electrical lead of claim 1, furthercomprising: a second electrode extending along the electrode headassembly and the lead body; a second conductor extending within a secondlead body lumen of the plurality of lead body lumens; and an attachmentmember coupling the second electrode and the second conductor andtransferring traction forces applied to the lead body to the electrodehead assembly.
 3. The medical electrical lead of claim 2, wherein theattachment member includes a receiving portion having an attachmentmember lumen receiving the second conductor, and the electrode headassembly includes a recess retaining the attachment member.
 4. Themedical electrical lead of claim 3, the receiving portion being one ofeither crimped, staked, welded or brazed to mechanically andelectrically coupled the second conductor to the attachment member. 5.The medical electrical lead of claim 3, wherein the attachment memberincludes a cross-groove receiving one or more coils of the secondelectrode.
 6. The medical electrical lead of claim 5, wherein the secondelectrode is welded or brazed within the cross-groove to couple thesecond electrode to the attachment member.
 7. The medical electricallead of claim 5, wherein the cross-groove is compressed about the secondelectrode to couple the second electrode to the attachment member. 8.The medical electrical lead of claim 3, wherein the attachment member isretained within the recess by a biocompatible plastic tube surroundingthe electrode head assembly.
 9. The medical electrical lead of claim 3,wherein the electrode head assembly includes a second recess retainingthe first conductor.